[css-cascade-5] Clarify revert-layer on style attr and keyframes. w3c#6743 w3c#6749

Author: fantasai

css-cascade-5/Overview.bs

@@ -1848,8 +1848,19 @@ Rolling Back Cascade Layers: the ''revert-layer'' keyword</h4>
 
 	Note: If there are no lower-priority declarations
 	in the same [=cascade origin=] as the ''revert-layer'' value,
-	the <a>cascaded value</a> will roll back to the previous origin,
-	just as for the ''revert'' keyword.
+	the <a>cascaded value</a> will roll back to the previous origin.
+
+	Note: The [=animation origin=] is not collapsed with the [=author origin=] for this purpose
+	as it is for ''revert'',
+	and thus effectively forms its own [=cascade layer=].
+	<a href="#style-attr">Element-attached styles</a>
+	likewise form their own [=cascade layer=];
+	however, since [=author origin=] [=important=] rules are sorted
+	between their [=normal=] and [=important=] levels,
+	an element-attached [=important=] ''revert-layer'' declaration will revert through
+	all [=author origin=] [=important=] declarations as well as the [=animation origin=]
+	along with its own [=normal=] declarations,
+	but not through any other [=author origin=] [=normal=] declarations.
 
 
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